This invention relates generally to manufacturing processes for fabricating semiconductor integrated circuit devices. More particularly, it relates to an improved method of applying a lower viscosity coating liquid onto a semiconductor wafer substrate so as to maintain the desired adhesion and defect characteristics thereof.
As is generally known to those in the semiconductor industries, there is a continuing trend of manufacturing semiconductor integrated circuits with higher and higher densities on a smaller chip area. As a consequence of this desire for large scale integration, this has led to a continued shrinking of the circuit dimensions and features of the devices so as to reduce manufacturing costs and to improve circuit functionality. The ability to reduce the size structures such as shorter gate lengths in field-effect transistors is driven by lithographic technology which is, in turn, dependent upon the wavelength of light used to expose the photoresist. Currently, optical steppers expose the photoresist using light having a wavelength of 248 nm is widely used in manufacturing, but a radiation having a wavelength of 193 nm is being experimented in research and development laboratories. Further, the next generation lithographic technologies will in all likelihood progress toward a radiation having a wavelength of 157 nm and even shorter wavelengths, such as those used in Extreme Ultra-Violet (EUV) lithography (.apprxeq.13 nm).
As the wavelength of the radiation decreases, such classic image exposure techniques cannot be used to satisfactorily generate the pattern linewidths in the photoresist of greater than 0.25 .mu.m (2500 .ANG.). This is due to the fact that the organic-based photoresist materials will become increasingly opaque to the radiation. In order to overcome this drawback, there has been developed in recent years the use of ultra-thin resist (UTR) coatings in order to maintain the desired characteristics of the masked photoresist structures (e.g., near vertical sidewalls for the resist profiles, maximum exposure/focus latitude). In the current state-of-the-art, integrated circuit manufacturers have been using in the resist process a resist coating having a standard photoresist thickness of more than 0.5 .mu.m (5,000 .ANG.) for 248 nm lithography and 0.4 .mu.m (4,000 .ANG.) for 193 nm lithography. Thus, a resist coating having an UTR thickness is considered to be resist films of less than 0.25 .mu.m (2500 .ANG.) in thickness.
However, the application of a UTR coating is not without any problems. In order to apply the UTR coatings having thicknesses of 2,500 .ANG. or less, the viscosity of the photoresist materials must be significantly less than those currently used in the state-of-the-art photoresists. The use of such lower viscosity photoresist materials suffers from the disadvantage that they exhibit poor adhesion to the substrates and high defect levels in the coated films when using the standard or conventional coating procedures.
Accordingly, there exists a need of developing a way of applying a lower viscosity photoresist material to the substrates but yet can still maintain the desired adhesion and low defect level characteristics of the photoresist film. This is achieved in the present invention by utilizing a priming step in which the substrate surface is pre-coated with a bonding agent for a short amount of time at room temperature prior to the step of applying a liquid solvent to the surface of the substrate.